Electric wheel drive systems used in off-highway machinery require a flow of coolant such as hydraulic oil to maintain an optimum operating temperature. Oil cooling is advantageous because it can provide both cooling and lubrication. Since churning losses can reduce efficiency, especially at higher speeds, dry sump systems are a preferred approach for implementing these cooling and lubrication systems.
Implementation of a dry sump system in a simple form requires providing a supply and a scavenge pump at each wheel motor site and providing a means for powering these pumps. To simplify the systems, the required pumps can be ganged together so that a single power source can be used, but providing this power source and controlling it adds complexity and is undesirable.